The present invention relates to a flow cell.
In liquid chromatography, a fluidic analyte may be pumped through conduits and a column comprising a material which is capable of separating different components of the fluidic analyte. Such a material, so-called beads which may comprise silica gel, may be filled into a column tube which may be connected to other elements (like a control unit, containers including sample and/or buffers) by conduits.
When a fluidic sample is pumped through the column tube, it is separated into different fractions. The separated fluid may be pumped in a flow cell in which the different components are identified on the basis of an optical detection mechanism.
U.S. Pat. No. 5,153,679 discloses an apparatus for measuring light absorbance in a liquid sample which includes a light source for directing light into a sample cell, a cylindrical sample cell, a light detector for measuring intensity of light emitted from the cell and focusing means for forming a tapered light beam to pass through the sample cell. The tapered light beam can be either a diverging beam or a converging beam through the cell. When the light beam is a diverging beam, a masking means is positioned downstream of the cell to assure that any light striking the cell wall is not directed to the light detector.
Further conventional flow cells are disclosed in US 2003/0076491, US 2008/0079942, US 2007/0097361, US 2007/0132230, US 2007/0132241, US 2007/0132229, and WO 2007/009492.
K. Mogensen, J. El-Ali, A. Wolff, J. Kutter, “Integration of polymer waveguides for optical detection in microfabricated chemical analysis systems”, Applied Optics, Vol. 42, No. 19, 2003, pp. 4072 to 4079, discloses multimode polymer waveguides and fiber-to-waveguide couplers integrated with microfluidic channels by use of a single-mask-step procedure, which ensures self-alignment between the optics and the fluidics.
Conventional flow cells may be complex in manufacture.
Typical dimensions of the flow path of a conventional HPLC-UV/Vis absorption cell, as stated in U.S. Pat. No. 5,153,679, are 10 mm length, 1 mm diameter and about 8 micro liters volume. The flow path is not always cylindrical, it may also have a conical shape, for instance a taper cell. The dimensions of these cells often require special machining methods in manufacturing, for example such as electric discharge machining, which has limited geometrical accuracy. But in order to avoid the undesired refractive index effects, as described in the source above, small tolerances are required. Spark eroding also can introduce unwanted electrode atoms, for example copper atoms, into the cell body material. The copper atoms can lead to spurious signals when the cell is used with extremely sensitive detectors, for example mass spectrometers.To achieve better chromatographic resolution in HPLC, capillary LC or CE, the cell volumes have to become smaller and hence their inside diameters. In U.S. Pat. No. 5,184,192 A, liquid waveguide cells with typical inside diameters in the range from 0.5 mm to 0.05 mm are described. The manufacturing of these type of cells with such small geometries and reflecting walls require special and complex procedures. Coatings of fluoropolymers like Teflon AF are used to achieve total internal reflection. The coatings are manufactured by series of filling the cell with a Teflon AF solution followed by drying and baking processes or by complex alternative methods.